The NUJ is challenging the right of the British Association of Journalists, a rival organisation set up by former NUJ general secretary Steve Turner, to represent Trinity Mirror staff.

A recognition deal between the BAJ and Mirror Group management for the Racing Post was set up last July, but challenged by the NUJ which lodged an appeal with the Central Arbitration Committee, the body that oversees trade union recognition, in September.

The NUJ lost the appeal on legal grounds and is seeking the judicial review in an attempt to overturn the CAC's findings.

The NUJ claims its rival had no "democratic" basis for representation, because the BAJ was handed the recognition deal through a voluntary arrangement with Mirror Group management last year.

The Racing Post is at the centre of the dispute, with the NUJ claiming the BAJ has no representation among journalists on the Trinity Mirror title.

"There are about 130 journalists working on the Racing Post and about 120 of them have signed a petition rejecting the BAJ," said the NUJ's national newspaper organiser, Barry Fitzpatrick.

"We're seeking to establish whether it [the BAJ] has the right to represent journalists, who should have the legal right to chose what union they want, rather than have one imposed on them."

The BAJ secured its representation of Mirror Group workers through a voluntary arrangement with management last year.

The legal challenge follows an unsuccessful appeal by the NUJ to the Central Arbitration Committee, which handles trade union recognition.

The CAC said Mirror Group executives had been able to "defeat what are, in all probability, the wishes of the majority of the relevant workforce by the simple expedient of concluding a voluntary recognition agreement with a wholly unrepresentative union".

However, the committee also said the Racing Post agreement was representative under law and dismissed the NUJ's claim.

The NUJ is also supporting a claim by journalists on other Mirror Group titles to have the BAJ derecognised.

Earlier this month the NUJ sent a petition with 75 signatures to the CAC in a bid to have its "unpopular" rival derecognised. The number of signatories to the petition has since risen to 100.

The petition claims the BAJ has done little to stem job losses at the Daily and Sunday Mirror and the People since it gained union recognition in 2001.

"The BAJ has been a disaster for Mirror Group journalists," said Terry Lloyd, a subeditor on the People.

"But, more than anything, this application is about democracy and giving journalists a say about which union they want to represent them."

The CAC is considering whether to order a workplace ballot to determine how much support there is among Trinity Mirror staff for the BAJ. If the committee determines there is not enough support, the NUJ will seek recognition.

Mr Fitzpatrick said the outcome of the Racing Post case would affect other Mirror Group titles.